1. Field of the Invention
The present invention relates to an electric motor of a stepping motor or a brushless motor or the like used for a drive source or the like of an electronic apparatus of a digital camera or a camera attached portable telephone, and an electronic apparatus having the electric motor.
2. Description of the Related Art
In a related art, an electric motor of a stepping motor or a brushless motor or the like is mounted to various electronic apparatus as a drive source or the like. For example, a stepping motor is excellent in terms of compatibility with a digital control system and, in recent times, has been frequently utilized as the drive source for driving a lens for focusing or zooming in an electronic apparatus of a digital camera or a camera attached portable telephone or the like. In recent years, further promotion of small-sized formation and reliability has been achieved for an electric motor mounted to an electronic apparatus in accordance with small-sized formation and precision formation of an electronic apparatus.
For example, there is proposed a stepping motor including a rotor having a rotating shaft, a stator covering the rotor, and a bearing fixed to a bearing frame portion provided at the stator for axially supporting rotatably the rotating shaft of the rotor and provided with a slider between the bearing and the rotor (refer to, for example, Patent Reference 1). According to the stepping motor, by using a washer having a projected portion brought into contact with the bearing frame portion as the slider, a friction load generated in accordance with rotation is reduced and wear of the rotor is prevented, and thrust rattle can be restrained from being brought about.
Further, as another example, there is proposed a stepping motor in which a rotor is constituted by a magnet in a cylindrical shape, and a molded member comprising a thermosetting resin for coupling the magnet and a rotating shaft and an end face thereof is provided with a heat resistant sliding member integrally molded with the magnet and the molded member (refer to, for example, Patent Reference 2) According to the stepping motor, by integrally molding the sliding member with the molded member of the rotor, resin burr can be reduced in being molded while functioning as the slider.
Patent Reference 1: JP-A-2000-4570
Patent Reference 2: JP-A-2002-199671
However, according to Patent Reference 1, in order to ensure a member dimension necessary for functioning as the slider, a space in correspondence therewith is needed between the bearing and the rotor. Therefore, there is a limit in achieving small-sized formation of a total of the electric motor in an axis line direction of the rotating shaft. Although it is also conceivable to reduce a member dimension of the slider or the bearing in order to achieve small-sized formation in the axis line direction, there is a concern of reducing a durability by reducing a strength thereof, or detaching the member from the rotating shaft in being impacted in being dropped or the like, and there is a limit in reducing the member dimension. Further, when the member dimension is reduced, a workable material is limited, and material cost, working cost are increased.
Further, since the space of providing the slider is needed as described above, a dimension in the axis line direction of the rotor is reduced relative to the stator. Therefore, a torque cannot efficiently be operated to the rotor by a magnetic field formed by the stator. Particularly, since there is a limit in reducing the member dimension of the slider as described above, the more small-sized is the total of the electric motor, the more reduced is the rate of the dimension in the axis line direction of the rotor relative to the stator to pose a problem of being inefficient.
Further, according to Patent Reference 2, the slider is rotated integrally with the magnet and the molded member constituting the rotor. Therefore, an effect of reducing a friction load generated between the bearing and the rotor is reduced as the slider. Further, it is necessary to reduce the bearing more than a diameter dimension of the slider so as not to be brought into contact with the molded member exposed at a surrounding of the slider in order to prevent a reduction in the torque by the friction load, and the slider is brought in to contact with a total of the bearing. Therefore, a reduction in the friction load cannot be achieved efficiently in the above-described constitution.